Though current vaccines reduce the impact of influenza, IAV remains a major human pathogen with an enormous global and domestic impact, causing 30,000 deaths and economic costs totaling tens of billions of dollars each year in the USA. Despite its remarkable impact on public health, we have only a limited understanding of the molecular mechanisms underlying viral pathogenesis and its ability to evade the immune response. In this project we are studying a number of aspects of the interaction between IAV and the host. Most of studies utilize the mouse model of infection but we have also examined transmission in guinea pigs. Our interests include understanding selection of antigenic variants in vivo, host-pathogen interactions in regulating anti-viral immunity, and the role of influenza protein in viral pathogenesis. Our current studies have been aimed at understanding the evolution of influenza virus transmissibility. Our studies in 2015 have found that NP is able to selectively control IAV gene packaging and balancing glycoprotein expression. The results suggest a role for incomplete gene packaging during host adaptation and transmission of the virus.